This invention relates to improvements in a rear suspension apparatus provided between the rear wheels and body of an automotive vehicle.
In a previously proposed conventional rear suspension apparatus for an automotive vehicle, the front- and rear-side portions of a wheel support member for supporting a rear wheel are supported on the vehicle chassis via respective resilient members, the elastic characteristics of these resilient members are specially selected, and use is made of the relationship between the lateral forces acting on the rear wheels and the elastic characteristics to perform toe-in control of the rear wheels.
An example of this prior-art arrangement is disclosed in the specification of Japanese Patent Application Laid-Open Publication (KOKAI) No. 60-148707, in which the ratio of the amount of flexibility of the resilient member for the front portion to that of the resilient member for the rear portion is set so as to become large when the action of the lateral force on the rear wheel is small in comparison with when the action of the lateral force is large. Such an expedient improves steerablity when large lateral forces are acting on the rear wheels.
Another example of the prior art is disclosed in the specification of Japanese Patent Application Laid-Open Publication (KOKAI) No. 60-148708, in which the ratio of the amount of flexibility of the resilient member for the front portion to that of the resilient member for the rear portion is set so as to become small when the action of the lateral force on the rear wheel is small in comparison with when the action of the lateral force is large. This prevents sudden reverse steering when a difference between lateral forces is great.
The abovementioned Japanese Patent Application Laid-Open Publication (KOKAI) Nos. 60-148707 and 60-148708 have been filed in the United States as U.S. Pat. No. 4,621,830, claiming the respective Convention priorities.
In the aforementioned prior art, consideration is given only as to how to perform control with regard to the lateral forces acting upon the rear wheels in a direction from the outward side to the inward side of the vehicle.
When making a maneuver such as a lane change at high velocity, the driver turns the steering wheel in one direction and then in the opposite direction in a short period of time. Consequently, as shown in FIG. 13, the design is such that when the front wheels are steered rightward, for example, as indicated at point A, the outer and inner rear wheels will have a tendency to toe in and toe out, respectively, due to the lateral forces acting upon them. (Note that "inner rear wheel" refers to the rear wheel on the inner side of a turn, while "outer rear wheel" refers to the wheel on the outer side of a turn.) Accordingly, in order to improve turnability, the wheel support is resiliently supported in such a manner that the outer rear wheel will be displaced in the toe-in direction upon receiving an inwardly directed lateral force. This fact indicates that the wheel is easily displaced in the toe-out direction with regard to an outwardly lateral force in the opposite direction, namely in a direction from the inward to the outward side of the vehicle. Next, when the vehicle is steered to resume traveling straight ahead, as indicated at point B, the rear inner wheel (which was the rear outer wheel at point A) maintains the toe-in tendency but the rear outer wheel (which was the rear inner wheel at point A) maintains the toe-out tendency due to a delay in response. As a result, in the conventional automotive vehicle, rear gripping force weakens at high velocities and steering readily loses stability.